1. Field of the Invention
The present invention relates to a backlight module and light guide plate thereof, and particularly to a high brightness backlight module and light guide plate thereof.
2. Description of Related Art
Conventional backlight modules for use in rear projection displays such as liquid crystal displays are classified into two types, the edge-type and the direct type, depending upon the position of the light sources in the displays. Edge-type backlight modules are usually used in liquid crystal displays because they save space due to their thinness.
One conventional edge-type backlight module has a structure as shown in FIG. 9. In this figure, the conventional backlight module 1 includes a light source 11, a light cover 12, a light guide plate 13, a reflective sheet 14, and a brightness enhancing film 15.
The light guide plate 13 comprises an incident surface 131 for receiving incident light emitted from the light source 11, a bottom surface 132 with a large number of fine dots 134 for reflecting and diffusing the incident light, and a top surface 133 for emitting light. The brightness enhancing film 15 has a plurality of micro-lens structures 151 disposed uniformly on its surface, which tend to collimate the light emitted from the top surface 133 of the light guide plate 13 toward a direction of a liquid crystal panel.
However, in the conventional backlight module 1 as described above, since a plurality of discrete elements are used, the light emitted from the light source to the liquid crystal panel passes through a number of light interfaces, so light energy is lost. Further, the backlight module is expensive due to the high cost of the brightness enhancing film used therein.
To solve the above problems, a backlight module 2 shown in FIG. 10, is described in U.S. Pat. No. 5,999,685. The backlight module 2 includes a light source 21, a light cover 22, and a light guide plate 23, wherein the light guide plate 23 comprises a bottom surface 233 with a number of printed-dots thereon (not shown) and a top surface 231 with a plurality of V-shaped grooves 232 therein. The V-shaped grooves 232 commonly have a vertex angle of 60 to 120 degrees, with the most effective vertex angle being 90 degrees.
The light guide plate 23 with the V-shaped grooves 232 combines the functions of the light guide plate 13 and the brightness enhancing film 15 of the FIG. 9 prior art, thereby avoiding use of the expensive brightness enhancing film 15, and decreasing the amount of elements in the module. The structure shown in FIG. 10, therefore, can cost less than the structure shown in FIG. 9 since the brightness enhancing film 15 is eliminated.
Usually, the light guide plate 23 is formed using the steps of: kneading liquid material; injecting the liquid material into a mold at high pressure using an injection molding machine; allowing the injected material to solidify by cooling; and extracting the light guide plate from the mold. A light guide plate having a shape corresponding to that of the mold is thus obtained.
However, in practice, controlling a precise vertex angle of the V-shaped grooves 232 to be 60–120 degrees as extracted from the mold, is difficult, and it is difficult to get the surfaces of the grooves to be smooth. Thus the brightness of the backlight module 2 is impaired.